Carbon Black is a finely divided form of carbon, produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar and in small quantities from vegetable oil. It is essentially composed of elemental carbon in the form of semispherical, colloidal particles coalesced into each other and forming mainly particle aggregates. Carbon black is a form of amorphous carbon that has a high surface area to volume ratio. The Carbon Black (CB) powders have a variety of applications ranging from tires to electrodes, pigments, cosmetics, plastics, paints etc. However, the grade of the powder required in each of these applications is different in terms of structure and composition. One of the primary requisite for specialty applications is the high purity of Carbon black powders in terms of Sulfur content as well as other metal ion contamination. One of the inherent problems with the Carbon Black manufacturing is the overall sulfur content in the raw materials which not only creates environmental hazards during the combustion processes of oils but also gets carried with the final Carbon Black powders. The presence of sulfur in the final product is detrimental to the quality especially for specialty applications. The Carbon Black Feedstock or Carbon Black raw material typically contains about 1-4% sulfur. About 40% of this sulfur gets retained into the final Carbon Black product during the manufacturing processes amounting to about 1.0 to 1.5% sulfur. This high sulfur impurity is detrimental for applications particularly as pigments, industrial electrodes, base coats, conductive coatings etc. In the insulating plastics industry, there is a need for low sulfur containing carbon black to enhance the insulating capability of the substance and make its surface more uniform. Essentially, the sulfur content required is less than 0.75% as per industry standards.
The prior art discloses various methods for sulfur removal such as hydro-desulfurization, adsorption, solvent extraction, bioenzymatic treatment, oxidation etc. However, these processes are applicable towards sulfur removal of petrochemical oils and liquid fuels in general.
The process for sulfur removal from petroleum oils is based on treatment of the oil by an alkali metal, especially sodium metal as the desulfurizing agent. In this process, the sulfur is primarily removed as a metal sulfide instead of the removal of the entire sulfur containing molecule. The sodium metal is generally used as pure metal or as an alloy, supported on inert species, or as dissolved in ammonia. In some processes, other sodium-based, compounds such as NaHS, NaNH2 are used for the desulfurization. However, these sodium-based desulfurization processes are associated with limitations such as low yield of desulphurized feed oil, formation of large amount of insoluble sludge, requirement of hydrogen and safety concerns. The inherent high viscosity of heavy oils and petroleum residues makes it difficult for the processing and separation operations before and after the desulphurization process. Thus, there is a substantial loss of feed oil during the process, especially during filtration or separation. Also, many of the sodium metal based processes for oil treatment use hydrogen at high pressures in combination to the sodium metal for desulfurization.
The above mentioned processes in literature for reducing the sulfur content are targeted at crude oils or for heavy oil up gradation. However, none of these processes have been attempted for desulfurization of solids materials such as Carbon Black powders. The removal of sulfur from solid powder materials such as Carbon black using sodium based desulfurization is hitherto unexplored.
Therefore, there is felt a need to develop a process for reducing sulfur from carbon black powder using sodium based desulfurization technology.